"Invalid battery" why do my old battery works but my new ones give this message?

[Android Central Question]

I have LG G5 I charge via outside battery charger and have two batteries to switch. Recently the newer battery fully charged showed 50% and short after the phone was started showed the message "Invalid battery" and shut down. I thought the battery have broke so I bought a new one. It worked perfectly for a week and showed the same: only 50% after fully charged and then "Invalid battery". Is this problem from the phone itself? All batteries were bought as original LG batteries and couldn't find physical differences between them.

 

[Rukbat]

The phone is 3 years old, so the "original LG batteries" are also 3 years old - and probably in pretty bad condition. That's one way they get us to buy new phones - they don't make new batteries for older phones.